linux-kernel - system stops sending IOs for long time

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Date:	Tue, 30 Oct 2007 18:59:03 +0200
From:	"saeed bishara" <saeed.bishara@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: system stops sending IOs for long time

Hi,
I have a performance issue with my system that runs samba server, once
in a while (6 seconds) I see that the throughput falls almost to to
zero when doing read for large file. I'm running kernel 2.6.22.10. I
don't see this issue when using kernel 2.6.12.

when observing the activity leds on my sata controller, I see that it
get off for about 1 second meaning no commands sent to the HDD for
that long time. I used the blktrace in order to have a look into the
IOs, and found that the system really stops sending commands for long
periods, here is the section of the blkparse that shows this problem:
  8,2    0    12747     5.550000000   328  D   R 108068834 + 512 [smbd]
  8,2    0    12748     5.550000000   328  D   R 108069346 + 512 [smbd]
  8,2    0    12749     5.550000000   328  D   R 108069858 + 512 [smbd]
  8,2    0    12750     5.550000000   328  D   R 108070370 + 512 [smbd]
  8,2    0    12751     5.550000000   328  U   N [smbd] 5
  8,2    0    12752     5.550000000     0  C   R 108068834 + 512 [0]
  8,2    0    12753     5.560000000     0  C   R 108069346 + 512 [0]
  8,2    0    12754     5.570000000     0  C   R 108069858 + 512 [0]
  8,2    0    12755     5.570000000     0  C   R 108070370 + 512 [0]
  8,2    0    12756     6.570000000     0  C   R 108066786 + 512 [0]
  8,2    0    12757     6.590000000   328  Q   R 108070882 + 8 [smbd]
  8,2    0    12758     6.590000000   328  G   R 108070882 + 8 [smbd]
  8,2    0    12759     6.590000000   328  P   N [smbd]
  8,2    0    12760     6.590000000   328  I   R 108070882 + 8 [smbd]
  8,2    0    12761     6.590000000   328  Q   R 108070890 + 8 [smbd]
  8,2    0    12762     6.590000000   328  M   R 108070890 + 8 [smbd]

any idea how to fix this issue?
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